Homeostasis and Transport Flashcards
How can ions/molecules be transported across cell membranes?
Movement of ions through channels into cells; pumping of ions/molecules against a concentration gradient (ATP always required against concentration gradient)
Three examples of passive transport?
diffusion, osmosis, facilitated diffusion
Two examples of active transport?
pumps and cotransporters
What are four factors that affect diffusion rate?
membrane permeability (how open channels are), concentration difference, electronegative potential across membrane, pressure (blood capillaries)
What is the extracellular concentration of Na+? Intracellular?
140 mM, 10mM
What is the extracellular concentration of K+? Intracellular?
4mM, 140mM
What is the extracellular concentration of Ca++? Intracellular?
2.4mM, 0.0001mM
What is the extracellular concentration of Cl-? Intracellular?
103mM, 4mM
Aquaporin is a transmembrane protein that increases the passive movement of what molecule across the plasma membrane?
Water, simple diffusion
What is an example of facilitated diffusion? What does it require, and how would you explain it?
Glucose transport inside pancreatic cells, it requires a carrier protein but does not require ATP to enter the cell (facilitated diffusion) because it is going down its concentration gradient
What is an example of a voltage gated channel that uses simple diffusion?
voltage gated Na+ channel in neurons
What is an example of a chemically gated channel?
Ach nicotinic receptors that require a conformational change when Ach binds, causes the cellular response
Resting membrane potential in neurons?
-70mV
maintained using selective permeability of ions and Na+/K+ ATPase
How is an action potential generated?
A. Depolarization to Threshold: Signaled by the brain, sodium leaks slowly until it reaches threshold ->When -60 miliwats (the threshold) is reached, action potential occurs
B. Activation of Sodium Channels and Rapid Depolarization: Sodium channels open ->Positive sodium ions rush in; Depolarization: Membrane potential moves positive; More sodium ions
Cells have different depolarization rates
C. Inactivation of Sodium Ions and Activation of Potassium Ions: Sodium channel closes ->Potassium channel opens ->Positive potassium ions rush in
Hyperpolarization (also known as Repolarization): Membrane potential moves negative; More potassium ions; While repolarizing, the levels go below the proper resting state of -70 miliwats ? In order to go into a resting state, it much be exactly -70 milliwatts
D. Both Channels are Closed -> Goes to a Resting State: Resting state is negative ->Refractory Period: When action potential occurs until resting state
What is vmax when related to facilitated diffusion?
Determined by concentration of carrier molecules & rate of movement of carrier molecules across channel. Simple diffusion has no vmax.
What is active transport?
The movement of ions or molecules across a cell membrane into a region of higher concentration, assisted by enzymes and requiring energy.
What are examples of primary active transport?
Na+/K+ ATPase, Ca++ ATPase, H+ pump
Requires energy in the form of ATP
What is secondary active transport? What are the two types?
Uses energy of one solute moving with the concentration gradient (created previously with primary active transport) to move another substance against the concentration gradient
- Cotransporters (symporters)- both ions in the same direction (one ‘uphill’ and one ‘downhill’)
- Exchangers (counter-transport)- antiport- ions move in separate directions (one ‘uphill’ and one ‘downhill’)
What are some examples of cotransporters?
Na/Glucose transporter Couples the Na+ gradient to move another molecule against its gradient). Na also transports amino acids and phosphate against their gradients.
What are some examples of exchangers?
Na/Ca exchanger, and the Na/H exchanger. Na moves into the cell bringing calcium and hydrogen out of the cell (against their gradient)
What is osmosis?
Solvent moving from area of high solvent concentration to low solvent concentration across semipermeable membrane
What is osmotic pressure?
Pressure required to maintain an equilibrium with no net movement of solvent
What is osmolarity?
osmoles of solute (can dissociate within solution) per liter of solution.
1 mole of NaCl yields 2 osmoles of solute particles in water
What happens if a cell is placed in a hypertonic solution?
Will cause water to rush out of a cell.
In many cases the solution (usually water) has a greater solute concentration (hyperosmotic) compared to the inside of a cell and where the solutes don’t easily/quickly equilibrate between solutions
What happens if a cell is placed in a hypotonic solution?
Will cause water to rush into the cell.
In many cases, the solution has a lesser solute concentration (hypoosmotic) compared to the inside of a cell and where the solutes don’t easily/quickly equilibrate between solutions
What happens if a cell is placed in a isotonic solution?
Nothing. Has the same solute concentration compared to the inside of a cell.
